Dynamic translating device



M y 1, 1938. c. RAYMENT El AL 2,118,862

DYNAMIC TRANSLATING DEVICE Filed Feb. 17, 1937 MAGNE T/C MA TERM L IN VEN TORS mvoolv c. RAYME/VT CLARENCE a. Honmw Patented May 31, 1938 UNITED STATES DYNAMIC TRANSLATING DEVICE Lyndon C. Bayment and Clarence 13. Howard,

Application February 17, 1937, Serial No. 126,170

Claims.

Our invention relates to translating devices, and more particularly to an electro-dynamic energy translation device which may be utilized for changing variations in electrical energy into 5 motion, or vice versa.

It is well known in the art that most electrical translating devices are reversible, that is, they may be used to change variations in electrical energy into motion, or may be utilized to translate motion into variations of electrical energy; therefore, while we have described our invention as being applied to a dynamic motor device for the specific purpose of obtaining a visible trace, it will be obvious that the same general structure is equally adaptable for use as a loud speaker or sound reproducer, as a microphone, or for any other purpose where such translators are com monly used.

In the prior application of Lyndon C. Rayment, Serial No. 61,067, filed January 2'7, 1936, en-

titled Recording system", the inventor utilizes a pen recording system, and the present application describes and claims a preferred form of Pen recorder for that system utilizing a particular type of dynamic drive.

One of the main problems in utilizing dynamic translators is to remove from the moving element resonance periods which might interfere with the proper response of the drive. In the usual type of dynamic drive it is customary to support the moving coil in a strong magnetic field by means of a resilient spider or support, and in order that the resonance periods introduced by the resiliency of such supports be made as few as possible, it has been the custom to mak the spider extremely flexible. In dealing with extreme low frequencies, however, such as are encountered in the recording of heart sounds as a visible trace, for example, it has been found that such resilient spiders mask, to an undesirable degree, the true record desired, and it is one of the objects of our present invention to provide a dynamic drive for a recorder, or for similar purposes. wherein no springs are used as a restoring means.

Among the other objects of our invention are: To provide a dynamic translator utilizing magnetic restoring forces; to provide an electrodynamic translating device utilizing magnetic centering; to provide a dynamic translating device operating without the use of resilient coil suspensions; and to provide a means and method of operating a dynamic translator having a natural period greatly removed from the frequencies translated by the device.

Other objects of our invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but we do not limit ourselves to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

In the drawing, Figure l is an end view of one preferred form of our invention, as applied to a visible recorder.

Figure 2 is a sectional view, partly in elevation, of the device shown in Figure l.

The theory and method of operation of dynamic speakers is well known in the art at the present time, so that it will not be necessary to go into the physics of the device here. The present invention deals solely with the suspension and control of the moving coil in a dynamic transiator, and the invention may be more fully understood by direct reference to the figures.

As is customary in the art, an intense ma netic field is produced by the use of a cylindrical casing i of magnetic material, having a central pole piece 2 extending along the axis of the easing and through an aperture in a top plate 3 to form an annular air gap i. A field coil 5 is wound around the central pole piece, and when energized will provide an intense radio magnetic field in the annular air gap i. An annular moving coil is positioned in the air gap, this cell com prising an annular frame 6 of insulating mate- I rial having wound thereon a coil 1 provided with leads 8. The coil portion is generally dimensioned so that the majority of its turns are within the intense magnetic field in the air gap. It s obvious that a permanent magnet of the proper strength may be used to produce the field, if desired.

In the usual type of dynamic assembly the moving coil is supported on a resilient spider, and it is here that we depart from the prior art. Our moving coil is fixed rigidly by means of bracket arms 9 to a thin-walled rod ll) of extremely light material, such as Dural", or a similar light material having negligible magnetic properties. This rod extends through the central pole piece 2 in a bore hole II. The rod ID as used is of extremely thin section, the thickness of the walls thereof being greatly exaggerated in the drawing.

The rod I0 is maintained exactly in the axis of the pole piece by means of end bearings l2 and I3. The end bearing I3 is positioned at the coil end of the device and is supported by a bracket l4, connected to the top plate. The opposite and bearing [2 is attached to the bottom of the cylinder i and supports the other end of tube Hi. We prefer/to make these bearings very narrow and to provide them with rounded edges contacting the rod It! in order that friction may be reduced to a minimum. We have also found it desirable to make these bearings of "selflubricated material from metal which has incorporated therein lubricating material, such as oil or graphite, and we also prefer to highly polish the surface of the tube in contact with the bearings. We have thus been able to make a bearing which will not chatter inuse, which has an extremely small frictional factor, and which requires no oil. However, we do not wish to be limited in any manner to the type of bear" ing described herein.

With the tube suspended in this manner, it is obvious that the moving coil may move back and forth within the air gap without touching the sides thereof, and with a minimum of interference. Ihe weight of all the moving parts is extremely small, due to choice of materials, and thus the inertia of the moving parts is maintained at a low value.

Thus far the device as described is fully designed to maintain the coil laterally centered in the annular air gap, but does not have any means to maintain the coil in any central position longitudinally of the central pole piece, nor is there yet any means for applying any restoring force when the coil is moved out of the air gap. In the usual dynamic setup the resiliency of the supporting spiders provides this restoring force. We have found, however, that this restoring force may be obtained by positioning on the central tube It a small amount of magnetic material, shown here in one preferred form as a thin cylinder 15 of magnetic material, fixedly positioned around the tube l so that one end of the magnetic cylinder will be substantially inthe plane of the top surface of the device adjacent the moving coil. While we do not wish to be limited, in any way, by the form or material utilized for this magnetic material, we have found that a thin tube of silicon steel, such as is used for transformer laminations, is eminently satisfactory for the type of recording device shown here. Other modifications will easily be apparent to those skilled in the art.

When the field coil is energized, a magnetic field of steady value is obtained across air gap 4. There is, however, at the same time, a leakage flux adjacent the center of pole piece 2, and the cylinder l5, which is of magnetic material, is positioned in this leakage flux at a point where equilibrium is obtained, i. e., the coil under the influence of the leakage flux on sleeve I will not be moved when the field is energized and deenergized, or, if the coil should happen to be in a position moving sleeve I5 away from this equilibrium point, the sleeve will cause the coil to move until sleeve I 5 reaches the equilibrium point again, the coil being otherwise unrestrained. Al ternating current through coil 1 will tend to move the coil and its attached sleeve in or out of the air gap, and thus move sleeve l5 away from the equilibrium point in either direction, and the magnetic force exerted by the field acting upon the sleeve will always restore the coil to its original equilibrium position. In other words, instead of depending upon a resilient support for obtaining our restoring force, we utilize a magnetic material floating in the magnetic field of the device to give us our restoring force. In this respect it will be noticed that the restoring force acts quite differently than does a resilient support. In a resilient support, the further the moving coil moves from its normal position within the air gap, the greater the restoring force becomes, whereas in the instant device the restoring force tends to become less, and thus allows a more faithful motion of the coil, particularly when low frequencies are to be translated or when wide amplitudes are encountered,

Une of the uses to which we have found our.

dynamic translator to be ideally adapted is the use as a direct recorder of electrical impulses, such as for the pulse graphs of electro-cardiographs, tape recorders for telegraph signals, etc, and we will describe the use of the device as a tape recorder. In the latter use we prefer to hinge a recording arm to the tube III by means of a pin 2i, and fulcrum the recording arm in a gimbal assembly, or Universal motion support. The recording arm then extends beyond the fulcrum point and carries an ink reservoir 23, terminating in a writing point 24 bearing lightly on a tape 25 which is progressed underneath the writing point in any convenient manner well known in the art. Thus, there will appear on the tape in response to motion of the moving coil an ink trace 26.

By utilizing the device described above, we have found, for example, that heart and pulse traces may be recorded with far greater fidelity than with the usual type oi resilient suspension, and the use of the magnetic restoring force has removed the resonance periods from the moving parts of the device to such a point that they affect, to a negligible degree, the accuracy of the trace.

We have also found that the device is eminently satisfactory for use as a microphone, when utilized in conjunction with a diaphragm or equivalent device. The device is also utilized as a loud speaker, with the proper cone or diaphragm attached, and in the latter instance it is far more effective on the lower frequencies than is the usual type of dynamic speaker wherein resilient supports are utilized.

We claim:

1. In a dynamic translating device having a movable coil positioned in an annular air gap formed between a central pole piece and a top plate, a motional assembly comprising a rod of non-magnetic material extending through an axial bore hole in said pole piece and free from the walls thereof, means for supporting said coil in said air gap by said rod, bearings adjacent the ends of said rod to permit said rod and coil to mote in and out of said air gap, and a centering member of magnetic material mounted on said rod adjacent the coil end of said pole piece.

2. In a dynamic translating device having a movable coil positioned in an annular air gap formed between a central pole piece and a top plate, a motional assembly comprising a rod of non-magnetic material extending through an axial bore hole in said pole piece and free from the walls thereof, means for supporting said coil in said air gap by said rod, bearings adjacent the ends of said rod to permit said rod and coil to move in and out of said air gap, a cylindrical member of magnetic material mounted on and surrounding said rod adjacent the coil end of said pole piece.

3. In a dynamic translating device having a movable coil positioned in an annular air gap formed between a central pole piece and a top plate, a motional assembly comprising a rod of non-magnetic material extending through an axial bore hole in said pole piece and free from the walls thereof, means for supporting said coil in said air gap by said rod, bearings adjacent the ends of said rod to permit said rod and coil to move in and out of said air. gap, and a thin cylinder of silicon steel mounted on and surrounding said rod adjacent the coil end of said pole piece.

4. In a dynamic translating device having a movable coil positioned in an annular air gap formed between a central pole piece and a top plate, a motional assembly comprising a rod of non-magnetic material extending through an axial bore hole in said pole piece and free from the walls thereof, means for supporting said coilin said air gap by said rod, a pair of thin section bearing plates pierced to provide bearings for opposite ends of said rod and positioned to permit said rod and coil to move in and out of said air gap, said bearings having a rounded surface presented to said rod thereby providing only a circular line contact therewith.

' 5. In a dynamic translating device having a movable coil positioned in an annular air gap formed between a central pole piece and a top plate, a motional assembly comprising a rod of non-magnetic material extending through an axial bore hole in said pole piece and free from the walls thereof, means for supporting said coil in said air gap by said rod, bearings adjacent the ends of said rod to permit said rod and coil to move in and out of said air gap, and a mass oi magnetic material attached to said motional assembly at a point where magnetic forces will automatically tend to retain said assembly at a point where said coil is in said air gap in the absence of other forces, and also to oppose movement of said assembly by said other forces.

- LYNDON C. RAYMEN'I.

CLARENCE B. HOWARD. 

